suzuki sidekick 91- transmition shift points
 

Hi-
I just bought a '91 Suzuki Sidekick at a car auction - great shape,
seems (sounds & feels) like it runs great.
Here my question... it's an automatic transmition - and is okay until
I get >60 mph.... it sounds like it should shift one more time - but
does not. The RPms stay between 3500-4000 whenever I'm over 60 MPH -
it does not go down??
Should there be one shift - or is this a symptom of this make & model.
What can I check???
thanks for your help - Cindy